182 THE NATURE AND ORIGIN OF LIFE 



long enough with relation to the individual to transmit at 

 once, by protoplasmic continuity, a rupture of equilibrium 

 produced at a point A to a remote point B in the individual. 

 We find elementary types of such an arrangement in 

 the lower animals. One of the most characteristic examples 

 is found in certain coleoptera described by Hertwig. Fig. 13 

 gives three samples of such protoplasmic continuity. 



D 



FIG. 13. 



In the first type (A) an epithelial cell has but one prolonga- 

 tion m, which, on account of the conditions existing in the 

 place where it penetrates, takes a contractile character 

 (remember what we have already said of the physiological 

 division of labour). 



In the second type (B) the contractile prolongation 

 has the look of a complete cell provided with a nucleus. 

 It is a veritable muscle united to an epithelium by a nerve. 



Finally, in the third type (C) a new cell b an inter- 

 mediate or nerve cell appears in the continuous traject 

 which unites the epithelial element a to the muscular 

 element c. 



In the higher animals an entire network of protoplasmic 

 elements lengthened out plays the conducting part between 

 remote points of the same individual. Some of these 

 elements are more than a metre in length ; and we can 

 understand, with respect to co-ordination, the extreme 



